Phosphorus-31 NMR study of the effects of hydrogen peroxide on young and old rat lenses

Lipids and the ocular lens

The unusually high levels of saturation and thus order contribute to the uniqueness of human lens membranes. In addition, and unlike in most biomembranes, most of the lens lipids are associated with proteins, thus reducing their mobility. The major phospholipid of the human lens is dihydrosphingomyelin. Found in significant quantities only in primate lenses, particularly human ones, this lipid is so extremely stable that it was reported to be the only lipid remaining in a frozen mammoth 40,000 years after its death. Unusually high levels of cholesterol add peculiarity to the composition of lens membranes. Beyond the lateral segregation of lipids into dynamic domains known as rafts, the high abundance of cholesterol in the human lens leads to the formation of patches of pure cholesterol. Changes in human lens lipid composition with age and disease as well as differences among species are greater than those observed for any other biomembrane. The relationships among lens membrane composition, structure, and lipid conformation reviewed in this article are unique to the mammalian lens and offer exciting insights into lens membrane function. This review focuses on findings reported over the last two decades that demonstrate the uniqueness of mammalian lens membranes regarding their morphology and composition. Because the membranes of human lenses do undergo the most dramatic changes with age and cataractogenesis, the final sections of this review address our current knowledge of the unusual composition and organization of adult human lens membranes with and without opacification. Finally, the questions that still remain to be answered are presented.

Effects of cataractogenesis on the CDP-choline pathway: increased phospholipid synthesis in lenses from galactosemic rats and 13/N guinea pigs

We investigated the effects of cataractogenesis on phospholipid (P-lipid) synthesis in sugar cataracts from galactosemic rats and in hereditary cataracts from 13/N guinea pigs. Cataractous lenses from rats fed a 50% galactose diet for 7 days were incubated 24 h with radiolabeled choline or ethanolamine and the P-lipids were extracted. The galactosemic cataracts synthesized twice as much phosphatidylcholine (PtdCho) as control rat lenses, and phosphatidylethanolamine synthesis also was increased. Similar analysis of cataractous lenses from 3-week-old 13/N guinea pigs showed a 3-fold increase in PtdCho synthesis compared with control lenses. In all cases, the P-lipid precursor pool was lower in cataracts than in control lenses. The increased P-lipid synthesis in these cataracts may represent a membrane repair response to cataractogenic stress.

Effects of cataractogenesis on the CDP-choline pathway: changes in ATP concentration and phosphocholine synthesis during and after exposure of rat lenses to sugars in vitro and in vivo

We measured choline influx and phosphorylation, ATP concentration ([ATP]), choline kinase activity and lens swelling during formation and partial reversal of sugar cataracts in rat lenses incubated with xylose or galactose and in lenses of galactosemic rats. [ATP] and phosphocholine (P-Cho) synthesis decreased about 60 and 40% after 4 h in normal rat lenses incubated up to 24 h in medium containing 30 mM xylose and partially recovered when the lenses were then removed from the xylose. Incubation with the somewhat less cataractogenic sugar galactose decreased P-Cho synthesis but had little effect on [ATP]. P-Cho synthesis decreased rapidly in the lenses of rats fed a 50% galactose diet, but began recovery by the third day on this diet. [ATP] decreased for at least 10 days during the galactose diet and did not recover, even with resumption of the control diet (50% starch) after 4 or 7 days. The results of in vitro and in vivo sugar cataractogenesis differed from each other in several respects, including effects on choline influx and the degree to which the changes were reversible. The in vitro and in vivo sugar cataracts, however, could both produce swelling and opacification of the lens and decreased P-Cho synthesis and [ATP]. Neither model caused a substantial change in the choline kinase activity (as measured in cell-free assays). The data did not generally support the hypothesis that decreased [ATP] causes decreased P-Cho synthesis.

The effect of ginkgo biloba extract on EEG spectra in experimental diabetes: no relation to lipid peroxidation

Forty four Swiss albino rats aged two months, weighing 180-250 g, were used in the experiment. They were divided into four equal groups as control, alloxan-diabetic, diabetic + GbE and control + GbE. After the onset of experimental period, diabetic + GbE and control + GbE groups received ginkgo biloba extract and the other groups were given saline solution for ten weeks. Diabetic and diabetic + GbE groups were made diabetic by injecting alloxan on 16th day. Spectral analysis of EEGs recorded from parietal lobes of all groups of rats were computed by Fast Fourier Transform (FFT) algorithm. Their amplitude maxima were found to occupy the frequency bands of 1-2, 2-4, 4-6, 6-8, 8-16 and 16-30 Hz. Significant amplitude increase was found in 1-2 and 2-4 Hz frequency bands in diabetic + GbE group compared with control, but no differences were found for other groups.